Question

A large boulder is ejected vertically upward from a volcano with an initial speed of 39.0m/s . Air resistance may be ignored.

(a) At what time after being ejected is the boulder moving at a speed 19.0m/s upward?

(b) At what time is it moving at a speed 19.0m/s downward?
a. V = Vo + g*t = 19 m/s.
39 - 9.8*t = 19
-9.8t = 19-39 = -20
t = 2.04 s.

b. V = Vo + g*t = -19 m/s.
39 - 9.8t = -19
-9.8t = -58
t = 5.92 s.

If the question is to determine the maximum height of the boulder, what would the answer be?

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